Method for producing high silicon steel, and silicon steel

ABSTRACT

Manufacture by rolling silicon steel having a silicon content of 3 wt % or greater and by rolling thin sendust sheet is implemented by powder metallurgical fabrication using powder as the starting raw material, and the average crystal grain size of the sheet-form sintered body or quick-cooled steel sheet is made 300 pm or less, whereby intra-grain slip transformation occurs after slip transformation in the grain boundaries, wherefore cold rolling is rendered possible. In addition, a mixture powder wherein pure iron powder and Fe—Si powder are mixed together in a prescribed proportion is fabricated with a powder metallurgy technique, and an iron-rich phase is caused to remain in the sintered body, whereby cold rolling is possible using the plastic transformation of those crystal grains. Furthermore, when a minute amount of a non-magnetic metal element such as Ti, V, or Al, etc., is added beforehand, it becomes easy to make the iron-rich phase and silicon-rich phase enter into solid solution during annealing, crystal grain growth can be promoted, the magnetic properties of the fabricated steel sheet become roughly equivalent to those of conventional ingot material, and silicon steel sheet exhibiting outstanding magnetic properties can be fabricated.

TECHNICAL FIELD

The present invention relates to improvements in a method ofmanufacturing high-silicon steel, that is, Fe—Si alloy steel calledsilicon steel or Fe—Si—Al alloy steel called sendust which has a siliconcontent of 3 to 10 wt %. More specifically, the present inventionrelates to a manufacturing method for high-silicon steel that is verydifficult to cold-roll into thin sheet, that is, for example, to amethod of manufacturing rolled silicon steel sheet by fabricating asintered body or melt ingot having an average crystal grain size is 300μm or smaller, and, by enhancing crystal grain boundary slip,cold-rolling the material as is, or to a manufacturing method forobtaining super-thin sendust sheet by fabricating a thin sheet-formsintered body made up of an iron-rich phase and a silicon-rich Fe—Sisolid solution phase, making cold rolling possible using the outstandingmalleability of the iron-rich phase crystal grains, then, after coldrolling, causing aluminum to adhere to both sides of the thin sheet andperforming heat treatment.

BACKGROUND ART

Currently, almost all of the rolled silicon steel sheet used widely invarious applications such as iron cores in transformers and rotatingmachines, magnetic shielding materials, and electromagnets ismanufacturing by repeatedly subjecting silicon steel ingots wherein thesilicon content in the iron is 3 wt % or lower to the processes of heattreatment, hot rolling, and annealing.

It is known that permeability is maximized in silicon steel when thesilicon content is around 6 wt %, but the rolling of silicon steel sheetwherein the silicon content is 3 wt % or greater in the iron has longbeen considered very difficult due to fractures occurring duringrolling.

In general, the average crystal grain size in melt ingots of siliconsteel having a silicon content of 3 wt % or greater in the iron isseveral mm or greater, and plastic transformation induced by rolling isprimarily caused by slip transformation inside the crystal grains.

In cases where the silicon content exceeds 3 wt %, however, the crystalgrains themselves become very hard or brittle, wherefore, in siliconsteel melt ingots having an average crystal grain size of several mm orgreater, cracks readily occur during rolling, irrespective of whetherhot rolling or cold rolling is used, and rolling itself becomesvirtually impossible.

This is why a method was proposed (K. Narita and M. Enokizono: IEEE.Trans. Magnetic. 14 (1978) 258) for adding magnetic impurities such asmagnesium and nickel to make the average crystal grain size in meltingots more minute. The problem with this method, however, is that thesemagnetic impurities reduce the magnetic properties of the silicon steelsheet, and so it has not come into wide use.

Another method has been proposed (Y. Takada, M. Abe, S. Masuda and J.Inagaki: J. Appl. Phys. 64 (1988) 5367), and implemented, formanufacturing silicon steel sheet having a desired composition, such assilicon steel sheet having a silicon content of 6.5 wt %, byimpregnating the silicon using a CVD (chemical vapor deposition) methodafter rolling a melt ingot containing 3 wt % silicon in the iron in aconventional process. CVD requires many processes and involves highcost, however, wherefore the applications thereof are naturally limited.

In silicon steel, moreover, when the silicon content is increased, theelectrical resistivity ρ of the silicon steel also increases, which isuseful in reducing eddy current loss, and is desirable in a softmagnetic material usable in high frequency areas, but this has not beenmade practical because of the problem of processability noted earlier.

On the other hand, the Fe—Si—Al alloy (sendust) that excels as a softmagnetic material of high permeability is a steel material thatordinarily has a higher silicon content than the silicon steel sheetnoted above, and the manufacture of thin sheet thereof has long beenconsidered very difficult due to its great brittleness and hardness.

For this reason, a method has been proposed (H. H. Helms and E. Adams:J. Appl. Phys. 35 (1964) 3) for manufacturing thin sendust sheet of 0.35mm or so thickness by first fabricating an ingot having lower ironcontent than the composition required for sendust, pulverizing this,adding iron powder to the pulverized powder to make the requiredcomposition, causing the iron powder to act as a binder, and thenrepeatedly rolling and heat-treating this material.

Methods which employ the powder metallurgy noted above suffer theproblem of reduced magnetic properties due to inadequate diffusion ofthe added element, however, and so have not come into wide use.

For this reason, crystals of sendust having few flaws are fabricated,these are thinly machine-cut, and vapor-deposited by sputtering on adesired substrate to form a sendust thin sheet, the outstandingfunctioning whereof is used in VCR magnetic heads.

The situation, in other words, is that, conventionally, the volume ofsendust thin sheet produced is very small, and the applications thereofare limited, due to the difficulty of mass-production which involvesmuch time and effort.

DISCLOSURE OF THE INVENTION

An object of the present invention is to implement the rolling ofsilicon steel having a silicon content of 3 wt % or greater which hasbeen conventionally considered impossible. To that end, another objectof the present invention is to provide a manufacturing method for rolledsilicon steel sheet, and rolled material, wherewith it is possible toeasily make the average crystal grain size of the pre-rolled siliconsteel sheet more minute, and wherewith the rolled material can becontinuously and uniformly cold-rolled, as is, without repeatedlysubjecting the silicon ingots to heat treatment, hot rolling, andannealing.

Another object of the present invention is to provide silicon steelwherewith it is possible, without impairing the magnetic propertiesproper to silicon steel, to sufficiently increase electrical resistivityρ and reduce eddy current loss.

Another object of the present invention is, in view of the currentsituation wherein laminated iron cores and the like cannot be configureddue to the difficulty of manufacturing sendust thin sheet, to provide amethod of manufacturing sendust thin sheet wherewith it is possible tomanufacture sendust thin sheet by cold rolling and obtain sendust thinsheet having very outstanding magnetic properties.

The inventors reasoned that cold rolling would be possible, when rollingsilicon steel sheet having a silicon content of 3 wt % or greater, byusing a sintered body or thin melt sheet having an average crystal grainsize made minute for the pre-rolled silicon steel material, andsignificantly improving grain boundary slip.

Similarly, the inventors reasoned that cold rolling would be madepossible by using, for the pre-rolled silicon steel material, a sinteredbody wherein an iron-rich phase was caused to remain, and causingplastic transformation utilizing the crystal grain malleabilityexhibited by the iron-rich phase.

The inventors, as a result of various investigations made concerningrolling material for silicon steel exhibiting good cold-rollingcharacteristics, based on the ideas stated in the foregoing, focused onthe average crystal grain size, and made sintered bodies andquick-cooled melts to fabricate silicon steel rolling material having anaverage crystal grain size of 300 μm or less, made more minute thanconventional silicon steel resulting from slow-cooling melts. Theylearned that rolling was possible by cold-rolling this, that theeffectiveness of making the grain size minute is realized regardless ofthe silicon content, being particularly effective at and above 3 wt %,and that rolling can be done comparatively easily by making the sheetthickness of the rolling material 5 mm or less and the parallelism 0.5mm or less.

Similarly, the inventors focused on the composition inside the crystalgrains, fabricated sintered silicon steel sheet wherein an iron-richphase with abundant malleability is caused to remain in a mixed phasehaving an iron-rich phase and a silicon-rich Fe—Si solid solution phase,unlike the crystal grain of the phase where, with conventionalslow-cooling of the melt, iron and silicon are caused to completelybecome a solid solution, and learned that rolling is possible bycold-rolling this.

The inventors also learned, in terms of the method for manufacturing asintered body, that it is possible to fabricate a sintered body havingthe desired minute average crystal grain size by using powder metallurgytechniques to sinter gas-atomized powder or water-atomized powder havinga prescribed composition. They further learned, in terms of the powdermetallurgy techniques, that it is possible to adopt a method wherein,after molding by metal injection molding, green molding, or slip-castmolding wherein a slurry form of the powder is made to flow in,sintering is done at a prescribed temperature, or a method whereinfabrication is effected by a hot molding method such as hot pressing orplasma sintering, etc.

The inventors further learned, in terms of a method for fabricating thinmelt sheet, that a method can be adopted wherewith, in order to make theaverage crystal grain size as minute as possible, the molten siliconsteel is made to flow into a water-cooled casting mold having a thincasting thickness and rapidly cooled.

The inventors also learned, in terms of the composition of the rollingmaterial, that by adding small amounts of Ti, Al, or V, etc., theaverage crystal grain size at the time of annealing, after rolling, isreadily coarsened, that it is possible to completely make the iron-richphase and silicon-rich phase a solid solution, and that thin rolledsilicon steel sheet can thus be obtained that exhibits outstandingmagnetic properties wherein the coercive force drops precipitously.

The inventors, having learned of the method of manufacturing rolledsilicon steel sheet described in the foregoing, confirmed an increase inelectrical resistivity ρ associated with high silicon content.Thereupon, they conducted various investigations on additive elementswith the object of finding a material wherewith eddy current loss couldbe further reduced, and learned that lanthanum is effective. Afterconducting further investigations, they learned that that, when siliconsteel is fabricated with a sintering method, oxides of lanthanum aredeposited in the crystal grain boundaries, and that, accordingly, theirobject can be realized.

The inventors also learned, in terms of a method for depositing thelanthanum oxides in the crystal grain boundaries, that, in addition tothe sintering method noted above, that that can be achieved by taking asilicon steel ingot containing lanthanum and subjecting it either torepeated hot rolling or to repeated hot forging.

The inventors, having learned of the method for manufacturing rolledsilicon steel sheet described in the foregoing, learned further that, bytaking silicon steel sheet obtained by cold-rolling material formed of asintered body or melt ingot, of silicon steel having a minute averagecrystal grain size, or silicon sheet obtained by cold rolling, using asintered body wherein an iron-rich phase is made to remain, andutilizing the grain boundary malleability exhibited by that iron-richphase, vapor-depositing aluminum under various conditions on both sidesthereof and then performing heat treatment, the aluminum diffuses fromthe surface thereof into the interior, thereby yielding sendust thinsheet having outstanding magnetic properties wherein magneticpermeability is dramatically improved over that of silicon steel sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph plotting the relationship between lanthanum contentand the electrical resistivity β of sintered silicon steel wherein thesilicon content is 6.5 wt %;

FIG. 2 is a graph plotting the relationship between iHc and lanthanumcontent, on the one hand, and the average crystal grain size in sinteredsilicon steel wherein the silicon content is 6.5 wt %, on the other; and

FIG. 3 is a set of cross-sections, with that in FIG. 3A representing inmodel form the pre-rolling structure of sintered silicon steelcontaining lanthanum according to the present invention, and that inFIG. 3B representing in model form the structure thereof afterannealing.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is characterized by the means that it adopts inorder to efficiently manufacture silicon steel sheet exhibitingoutstanding magnetic properties, namely means for making cold rollingpossible by fabricating by powder metallurgy, using powder as theinitial raw material, and making the average crystal grain size of asheet-form sintered body or quick-cooled steel sheet 300 μm or less,thereby effecting crystal grain boundary slip transformation, andthereafter effecting intra-grain slip transformation, or means formaking cold rolling possible by fabricating, by powder metallurgy, apowder mixture wherein pure iron powder and Fi—Si powder are mixed in aprescribed proportion, and causing an iron-rich phase to remain in thesintered body, thereby effecting plastic transformation in the grainboundaries.

Sintered silicon steel resulting from the sintering of silicon steelpowder to which lanthanum has been added has a structure whereinlanthanum oxides (containing La₂O₃ and non-stoichiometric lanthanumoxides) are deposited in the crystal grain boundaries. This crystalgrain boundary phase is formed of highly insulative lanthanum oxides, asa consequence whereof the electrical resistivity ρ or the lanthanumsintered silicon steel becomes greater than in conventional siliconsteel.

The radius of the La³+ ion (1.22 Angstroms) is larger than either theradius of the Fe³+ ion (0.67 Angstrom) or the radius of the Si⁴+ ion(0.39 Angstrom). For that reason, it is believed that lanthanum hardlyforms a solid solution at all in the silicon steel matrix, that it isreadily deposited in the crystal grain boundaries by sintering, and thatit forms lanthanum oxides in the grain boundaries.

While La³+ is a rare earth element ion, it does not maintain a magneticmoment, and therefore neither functions as a magnetic impurity norimpairs the magnetic properties of the lanthanum sintered silicon steel.On the contrary, the addition of lanthanum makes the average crystalgrains of the sintered silicon steel coarser in the annealing process,and is known also to reduce coercive force.

In FIG. 1 is plotted the relationship between lanthanum content andresistivity β when the silicon content is 6.5 wt %. From FIG. 1 it maybe seen that a high level of resistivity β is indicated for lanthanumsintered silicon steel, a level that is from several times to nearly tentimes that of sintered silicon steel to which lanthanum is not added.

In FIG. 2 is plotted the relationship between lanthanum content, on theone hand, and post-sintering average crystal grain size and coerciveforce iHc, on the other, when the silicon content is 6.5 wt %. From FIG.2 it may be seen that the lanthanum-containing silicon steel of thepresent invention has a larger average crystal grain size than doessintered silicon steel to which no lanthanum is added, and that itexhibits outstanding magnetic properties.

Raw Materials Used in Fe—Si Alloy

In the present invention, the silicon steel is characterized by the factthat the composition of the silicon steel material in view is aprescribed composition wherein the silicon content in the iron is from 3to 10 wt %. That is, because rolling conventionally could not be donewith a silicon content of 3 wt % or greater, what is in view in thepresent invention is to make the silicon content of 3 wt % or greater.However, when 10 wt % is exceeded, the decline in flux density in thematerial is pronounced, wherefore the range is made 3 to 10 wt %.

A desirable range for lanthanum content is 0.05 wt % to 2.0 wt %. Whenthe lanthanum content is less than 0.05 wt %, the quantity of lanthanumoxides deposited in the grain boundaries is insufficient, and the effectof increasing the electrical resistivity is virtually not evidenced.When the lanthanum content exceeds 2.0 wt %, however, the processabilityof the silicon steel declines, making it very difficult to fabricatesilicon steel sheet by cold rolling. From the perspective of making theresistivity or specific resistance larger, a more preferable range oflanthanum content is 1.0 wt % to 2.0 wt %. The most desirable range forlanthanum content is 1.2 wt % to 1.5 wt %.

For the purpose of realizing magnetic properties, the silicon content inthe lanthanum-containing silicon steel should be 3.0 wt % to 10 wt %,but more preferably 5.0 wt % to 8.0 wt %. It is also possible to makethe silicon content less than 3.0 wt % in order to obtain silicon steelof high resistivity ρ.

In the present invention, when Ti, Al, and V are added at 0.01 to 1.0 wt% as impurity elements in the silicon steel material, either for thepurpose of promoting growth in the crystal grain size during annealingafter cold rolling, or for the purpose of making the iron-rich phase andsilicon-rich phase a complete solid solution, rolled silicon steel sheetexhibiting good magnetic properties is obtained. The composition andquantities of the additives may be suitably selected according to theapplication. When the Ti, Al, and V content is less than 0.01 wt %, thegrain growth effect is inadequate, whereas when 1.0 wt % is exceeded,the magnetic properties decline, wherefore the range is made 0.01 to 1.0wt %.

For the raw material here, either gas-atomized powder or water-atomizedpowder containing the components noted above is suitable in the case ofa sintered body, with an average crystal grain size of 10 to 200 μmbeing desirable. With an average crystal grain size of less than 10 μm,the density of the sintered body is enhanced, but a large volume ofoxygen is contained in the powder itself, which tends to cause crackingduring cold rolling and also causes a deterioration in magneticproperties.

It is also possible, to use a complex powder wherein silicon powder ismechanically coated onto the surface of the iron powder or otherreducing iron powder by a mechanofusion system or the like, or a complexpowder that is the reverse thereof, or a complex powder wherein thesilicon powder coating the iron powder is further coated with carbonyliron powder, or, alternatively, a mixed powder wherein Fe—Si compoundpowder and iron powder are mixed.

When the average crystal grain size of the sintering raw materialexceeds 200 μm, the sintered body tends to become porous and thesintering density declines, which also causes cracking during coldrolling. Accordingly, the average crystal grain size should be from 10to 200 μm. The quantity of oxygen contained in the raw material powderused should be small, the smaller the better, and preferably at leastbelow 1000 ppm.

In the present invention, the method for fabricating the sintered bodyhaving the desired minute average crystal grain size requires sinteringeither gas-atomized powder or water-atomized powder having thecomposition prescribed in the foregoing, by a powder metallurgytechnique.

When the material is fabricated from a melt ingot, if mixing and meltingis done so that the composition noted above is realized, there are noparticular limitations on the raw material used. It is especiallydesirable to employ quick cooling, as described below, in order toobtain an average crystal grain size of 300 μm or less. In order tocause lanthanum to be contained, either an Fe—Si—La compound orFe—Si—La₂O₃ is melted and forged into an ingot. After that, the ingot issubjected to repeated hot rolling or repeated hot forging to diffuse theLa₂O₃ into the grain boundaries.

In the present invention, in order to obtain a sintered body consistingof an iron-rich phase and a silicon-rich Fe—Si solid solution phase, apowder containing more silicon than in the desired composition isdesirable for the raw material, either a gas-atomized powder of an Fe—Sicompound of a brittle and easily crushed composition, or a mixed powderwherein a carbonyl iron powder is mixed in a prescribed proportion witha powder made by coarse-crushing and then jet-mill pulverizing an ingothaving that composition. When the silicon content in the crystallinephase of the sintered body exceeds 6.5 wt % it is called silicon-rich,and when it does not exceed 6.5 wt % it is called iron-rich.

For the Fe—Si compound used, β-phase Fe₂Si compounds, ε-phase FeSicompounds, and ζβ-phase FeSi₂ compounds are brittle and easily crushed,and therefore particularly desirable.

It is preferable that the silicon content in the Fe—Si compound be from20 wt % to 51 wt %. When the silicon content exceeds this range, thecompound is very easily oxidized, cracking readily occurs duringsubsequent cold rolling, and a deterioration in magnetic properties isinduced. For the same reason, it is desirable that the lanthanum contentbe set below 11 wt %.

When the average crystal grain size in the Fe—Si compound powder is lessthan 3 μm, the powder itself contains a large volume of oxygen, and thesintered body becomes hard or brittle, whereupon cracking readily occursduring cold rolling and the magnetic properties deteriorate. When theaverage crystal grain size exceeds 100 μm, the sintered body tends tobecome porous and the sintering density declines, constituting a causeof cracking during cold rolling. Accordingly, the best range for theaverage crystal grain size is 3 to 100 μm.

For the carbonyl iron powder, on the other hand, anything can be used,but it is preferable to use a commercially marketed powder having agrain size of 3 to 10 μm containing as little oxygen as possible. In anyevent, the less the oxygen content in the mixed powder of the ironpowder and Fe—Si compound powder the better, and that content shouldpreferably be at least below 3000 ppm.

Pre-Rolled Silicon Steel

A powder metallurgy technique can be used in fabricating the sinteredbody for the rolling material, but it is desirable that that method beone which fabricates a sintered body either by metal injection molding,green molding, or slip casting, etc., or by a hot molding method such ashot pressing or plasma sintering.

More specifically, metal injection molding, green molding, and slip-castmolding are methods wherein silicon steel powder is molded after abinder has been added. After the molding, the binder is removed andsintering is performed. With the hot rolling methods, the raw materialpowder is placed in a carbon metal mold and simultaneously molded andsintered under pressure while hot (1000° C. to 1300° C.).

In general, silicon steel powder of the stated composition is veryreadily oxidized due to the silicon content, and is particularlysusceptible to oxidation and carbonization when a binder is used in themolding, wherefore binder removal and atmosphere control duringsintering are indispensable. Oxidized or carbonized sintered bodiesbecome hard and brittle, moreover, so that cracking occurs when thematerial is cold-rolled and the magnetic properties after annealingexhibit pronounced deterioration. For these reasons, it is desirablethat, the oxygen content and carbon content in the sintered body bebelow 4000 ppm and below 200 ppm, respectively, and preferably below2000 ppm and 100 ppm, respectively.

The sintering temperature will differ depending on the composition,average crystal grain size, and molding method, etc., but, in general,sintering should be performed, according to the molding method, in aninert gas atmosphere, in a hydrogen gas atmosphere, or in a vacuum, at atemperature suitably selected between 1100° C. and 1300° C. Ifdeformation during sintering is not prevented to the extent possible,that will cause cracking to develop during cold rolling.

In particular, because an iron-rich phase exhibiting abundantmalleability is caused to remain after sintering, it is important thatsintering be done at a temperature that is slightly lower thanconventional sintering temperatures. Also, because lanthanum isintroduced to realize a further increase in the electrical resistivityρ, it is preferable that the sintering be done at a temperature that is100° C. or so lower than the sintering temperature used for ordinarysilicon steel. If every effort is not made during sintering to preventdeformation during sintering, and parallelism is not realized at 0.5 mmor lower per 50 mm of length, cracking will result during cold rolling.

Sintered silicone steel containing lanthanum has a structure whereinlanthanum oxides 32 are deposited in the grain boundaries of the Fe—Sicompound crystal grains 30, as diagrammed in FIG. 3A.

With molten silicon steel material, on the other hand, after being mixedto the prescribed composition and high-frequency melted, the moltensilicon steel is made to flow into a water-cooled casting mold having athin casting thickness of 5 mm or less, quick-cooled, and formed intosilicon steel sheet having a minute crystal grain size. It isparticularly easy to fabricate the silicon steel material of minutecrystal grain size when the thickness is made thin.

Rolling

Silicon steel has the properties of being harder and more brittle thanordinary metals, wherefore it is necessary to change the roller diameterand circumferential speed used in cold rolling depending on thepre-rolled sheet thickness and parallelism. In other words, if thepre-rolled sheet thickness is thick and parallelism is poor, rollingmust be done with a small roller size and low circumferential speed.

Conversely, if the sheet thickness is thin and parallelism is good,those conditions can be considerably relaxed. In the case of hotrolling, in particular, the silicon steel sheet becomes susceptible toplastic deformation, so that the roller diameter and circumferentialspeed conditions can be greatly relaxed as compared to the case of coldrolling. It is effective to perform hot rolling prior to cold rolling,but unless cold rolling is performed finally, thin film rolling isimpossible because the surface layer oxidizes and the magneticproperties deteriorate.

In the present invention, the average crystal grain size in the siliconsteel is made 300 μm or less and the pre-rolled sheet thickness 5 mm orless. When the thickness of the sintered body exceeds 5 mm, the rollingstress (pulling stress) acts only on the surface and no stress isimposed internally in the sintered body, wherefore cracking occurs. Whenthe thickness is 5 mm or less, however, the stresses imposed on thesurface and internally are uniform and rolling is made possible.

In the present invention, in the case of silicon steel sheet containingan iron-rich phase, with silicon steel sheet wherein the pre-rolledsheet thickness is 5 mm or less and the parallelism is 0.5 mm (per 50 mmin length) or less, cold rolling can be performed with no crackingwithout employing an annealing process during the cold rolling if theroller diameter is 80 mm or less and the roller circumferential speed is60 mm/sec or less.

In the present invention, if the thickness of the silicon steel sheet ismade even thinner at 1 mm or less, the rolling efficiency and thicknessdimension precision will be improved by rolling with rollers having aroller diameter that is even smaller, and cracking will be less likelyto develop.

When the average crystal grain size of the pre-rolled silicon steelexceeds 300 μm, cracking Develops during rolling irrespective of rollerdiameter or roller circumferential speed. Also, the fabrication ofsilicon steel sheet having an average crystal grain size of less than 5μm is possible only with a powder metallurgical sintering method, whichis a method wherein sintering is done with either the sinteringtemperature lowered or the molding temperature lowered. With eithermethod, however, a sintered body is obtained which has high porosity,wherefore cracking always develops during rolling.

In cases where the iron-rich phase in the silicon steel sheet disappearsand complete solid solution is attained, in particular, cracking willdevelop during rolling irrespective of roller diameter and rollercircumferential speed. Also, when the silicon content in the ironexceeds 10 wt %, it becomes difficult to cause the iron-rich phase toremain in the silicon steel sheet, and almost all of it becomes a solidsolution, wherefore cracking will always develop during cold rolling.

Also, with the silicon steel sheet rolled with the method of the presentinvention described in the foregoing, post-rolling machining by cuttingmachine or punching machine is possible, thereby facilitating themanufacture of products of various shapes.

The rolled silicon steel sheet according to the present invention,unlike ordinary directional silicon steel sheet wherein the (110) faceis made the aggregate structure, has the characteristics of directionalsilicon steel sheet wherein the (100) face is made the aggregatestructure.

Annealing

The annealing of the silicon steel sheet according to the presentinvention is done in order to enhance the magnetic properties afterrolling completion, to cause the iron-rich phase and silicon-rich phaseto enter completely into a solid solution, and to make the crystalgrains coarser. In other words, whereas conventionally the annealing ofrolled silicon steel sheet is always performed after rolling a number oftimes to prevent cracking during rolling, in the present invention, thisannealing is done with the aim of coarsening the crystal grain size forthe purposes of reducing the crystal grain boundaries that constitute abarrier to magnet wall movement, and reducing coercive force to improvepermeability and reduce iron loss.

Also, lanthanum sintered silicon steel, after annealing, exhibits astructure, as diagrammed in FIG. 3B, wherein the lanthanum oxides 32 aredeposited more abundantly in the grain barriers of the Fe—Si compoundcrystal grains 30 that have, grown more than prior to annealing.

The temperature for this annealing will differ depending on the rollingratio (post-rolling sheet thickness/pre-rolling sheet thickness×100(%))and the average crystal grain size. The annealing temperature is alsoinfluenced by non-magnetic element additives and the amounts thereofadded. Nevertheless, in the present invention, with an average crystalgrain size of 300 μm or smaller, a temperature range of 1150 to 1250° C.is suitable for rolled steel sheet having a comparatively small averagecrystal grain size and a high rolling ratio, while, conversely, forrolled steel sheet having a comparatively large average crystal grainsize and low rolling ratio, a slightly lower temperature range of 1100to 1200° C. is suitable.

If this annealing temperature is too high, the crystal grains exhibit anexcessive and abnormal growth and the steel sheet becomes very brittle.If, conversely, the temperature is too low, no crystal growth isrealized and the magnetic properties are not enhanced. Hence the besttemperature range is 1100 to 1250° C. as noted above. The averagecrystal grain size can be grown to approximately 0.5 to 3 mm byannealing at such temperatures. It has been confirmed that the magneticproperties obtained by this annealing are close to those of ordinaryingot material.

In the case of silicon steel sheet having an iron-rich phase, atemperature range of 1200 to 1300° C. is suitable for rolled steel sheetannealed at low temperature with a high rolling ratio, while,conversely, for rolled steel sheet annealed at high temperature androlled with a low rolling ratio, a slightly lower temperature range of1150 to 1250° C. is suitable.

If this annealing temperature is too high, the crystal grains exhibit anexcessive and abnormal growth and the steel sheet becomes very brittle.If, conversely, the temperature is too low, the iron-rich phase andsilicon-rich phase do not enter into solid solution and no crystalgrowth is realized, so that the magnetic properties are not enhanced.Hence the best temperature range is the temperature range noted above.

By annealing with the temperatures noted above, the iron-rich phase andsilicon-rich phase can be made to completely enter into a solidsolution, and the average/crystal grain size thereof can be grown toapproximately 0.5 to 3 mm. It has been confirmed that the magneticproperties obtained by this annealing are close to those of ordinaryingot material.

The annealing temperature will also be influenced by the lanthanumcontent and silicon content. When silicon steel sintered at acomparatively low temperature (1000 to 1100° C., for example) is rolledwith a rolling ratio of 70 to 90% or so, the preferable range ofannealing temperatures is 1200 to 1300° C. When silicon steel sinteredat a comparatively high temperature (1150 to 1250° C., for example) isrolled with a rolling ratio of 50 to 70% or so, on the other hand, thepreferable range of annealing temperatures is 1150 to 1250° C. When theannealing temperature is too high, the crystal grains grow abnormally,causing the silicon steel to become very brittle. Conversely, when theannealing temperature is too low, the lanthanum oxide deposition andcrystal grain growth become inadequate, wherefore the resistivity β andmagnetic properties are not sufficiently improved. The annealing timeshould be appropriately selected within a range of 1 to 5 hours, forexample.

Because the lanthanum oxide deposition and crystal grain growth areadequately effected simultaneously by annealing, the resistivity ρ orthe lanthanum-containing silicon steel increases to a level close tofrom several to ten times that realized when no lanthanum is added, andthe crystal grain grows to an average crystal grain size ofapproximately 0.5 to 3 mm. The magnetic properties of thelanthanum-containing silicon steel, moreover, become close to those ofordinary ingot material.

In the present invention, furthermore, the silicon steel sheet, afterrolling, can be cut or punched, etc., and products of various shapes canbe fabricated according to various applications. Thus the advantage isrealized of being able to fabricate, at low cost, silicon steel sheethaving good characteristics and high dimensional precision.

Moreover, because the rolled silicon steel sheet of the presentinvention is directional silicon steel sheet wherein the (100) face ismade the aggregate structure, it exhibits great permeability andmagnetic flux density as compared to non-directional silicon steelsheet.

The rolled silicon steel sheet, lanthanum-containing sintered siliconsteel, and forged silicon steel according to the present invention canbe widely used in the various applications in which currently existingsoft-magnetic material is used. In addition to being used in themagnetic material pieces at the ends of electromagnets and permanentmagnets (pole pieces), these materials are very suitable for use in suchapplications as MRI yoke elements, transformers, motors, and yokes.Fe—Si—Al Alloy

In the present invention, it is desirable that the silicon steel used asa raw material contains 8.3 to 11.7 wt % silicon and, and that thealuminum content be 0 to 2 wt % aluminum as its required composition. Interms of the raw material powder used here, as noted earlier, there isthe method of using a mixture powder wherein either iron powder andFe—Si powder, or iron powder and Fe—Si—Al powder, are mixed in aprescribed proportion, or, alternatively, the method of using an Fe—Sicompound or Fe—Si—Al compound powder having the prescribed composition.

For the raw material of the mixture powder noted above, a powdercontaining more silicon than in the desired composition is desirable,being either a gas-atomized powder of an Fe—Si compound of a brittle andeasily crushed composition, or a mixed powder wherein a carbonyl ironpowder is mixed in a prescribed proportion with a powder made bycrushing and then jet-mill pulverizing an ingot having that composition,or, alternatively, a powder containing more silicon than in the desiredcomposition, being either a gas-atomized powder of an Fe—Si—Al compoundof a brittle and easily crushed composition to which a minute amount ofaluminum has been added, or a mixed powder wherein a carbonyl ironpowder is mixed in a prescribed proportion with a powder made bycrushing and then jet-mill pulverizing an ingot having that composition.

For the Fe—Si—(Al) compound used, β-phase Fe₂Si compounds, ε-phase Fe—Sicompounds, and ζβ-phase FeSi₂ compounds are brittle and easily crushed,and are therefore desirable. It is preferable that the silicon contentin the Fe—Si compound be from 20 wt % to 51 wt %. When the siliconcontent is outside of this range, the material is very easily oxidized,and the magnetic properties are caused to deteriorate. It is preferablethat the aluminum content in the Fe—Si compound be from 0 to 6.0 wt %.When the aluminum content is outside of this range, cracking readilyoccurs during cold rolling and oxidation occurs even more readilyleading to a deterioration in the magnetic properties.

A range of 3 μm to 100 μm is most desirable for the average crystalgrain size in the Fe—Si compound and Fe—Si—Al compound. When the averagecrystal grain size is less than 3 μm, the powder itself tends to containa large volume of oxygen, whereupon the magnetic properties deteriorate.When 100 μm is exceeded, on the other hand, the sintered body tends tobecome porous and the sintering density declines, causing cracking tooccur during cold rolling.

The conditions for manufacturing the pre-rolled silicon steel of thesintered body or molted steel using the raw materials noted above are asstated in the foregoing and the rolling conditions are likewise asstated in the foregoing.

The method for impregnating the rolled silicon steel sheet made from theFe—Si alloy obtained with aluminum is to apply and make a film of thealuminum by vacuum deposition, sputtering, or a CVD method or the likeso that the prescribed post-diffusion composition is realized. Thequantity of aluminum applied and made into a film is appropriatelydetermined so that the final composition after diffusion becomes 2 to 6wt % of aluminum, 8 to 11 wt % of silicon, and the remainder iron.

The conditions for the application and film making noted above differaccording to the thickness and composition of the rolled silicon steelsheet and the vapor deposition method used, but the aluminum will bemore likely to diffuse more evenly, and the magnetic properties morereadily enhanced, if direct vapor deposition is imposed on the siliconsteel sheet the surface whereof has been cleaned after cold rolling. Inother words, because the crystal grain size after rolling is smallerthan the crystal grain size after annealing, and residual crystaldistortion is greater, the aluminum will more readily diffuse in thegrain boundaries.

In addition, the rolled silicon steel sheet according to the presentinvention, unlike ordinary ,directional silicon steel sheet wherein the(110) face is made the aggregate structure, has the characteristics ofdirectional silicon steel sheet wherein the (100) face is made theaggregate structure, and the rolled surface is not the most densesurface, wherefore an advantage is realized in that diffusion in thecrystal grains occurs readily during heat treating after vapordeposition.

The annealing of the silicon steel sheet to which aluminum is appliedaccording to the present invention is performed for the purpose ofcausing the vapor-deposited aluminum, for example, to diffuse andpermeate into the interior of the steel sheet, and to fabricate thinsendust sheet having as uniform a composition as possible.

The annealing heat treatment temperature must be suitably selectedaccording to the composition of the silicon steel sheet, the amount ofaluminum applied, and thee average crystal grain size prior to rolling.When the heat treatment is done in a vacuum, this temperature should beset lower, at 1000 to 1100° C., whereas, when the heat treatment is donein an inert gas atmosphere, the temperature should be slightly higher,at 1100 to 1200° C., and, after the aluminum has diffused and permeated,the temperature should be raised to 1200 to 1300° C. and the crystalgrain size made coarser in a heat treatment process that follows afterthe aluminum impregnation heat treatment.

If this annealing temperature is too high in a vacuum, the aluminum willbe vaporized from the steel sheet and have difficulty diffusing andpermeating. If the temperature after the aluminum has diffused is toohigh, the crystal grain will exhibit excessive and abnormal growth andthe steel sheet will become very brittle. If, contrariwise, thetemperature is too low, grain growth will not occur and the magneticproperties will not be improved. Hence the temperature ranges notedabove are ideal. The average crystal grain size can be grown toapproximately 0.5 to 3 mm by annealing at the temperatures noted above.It has been confirmed that it is possible, by such annealing, to achievemagnetic properties in the thin sendust sheet that are close to those ofordinary ingot material.

Conventionally, sendust alloys, due to their hardness and brittleness,have been considered to be difficult to roll and impossible to make intothin sheet-form material. However, with the present invention, coldrolling is made possible by using, for the starting raw material, eithera mixture powder made by mixing either iron powder and Fe—Si powder, oriron powder and Fe—Si—Al powder, in prescribed proportions, or,alternatively, using a powder having the desired composition, andfabricating thin sheet to a thickness of 5 mm or less wherein aniron-rich phase exhibiting abundant malleability is made to remain.

With the present invention, furthermore, after depositing and making afilm of aluminum on both sides of the rolled silicon steel sheet asdescribed in the foregoing heat treatment is imposed to effect aluminumdiffusion and to coarsen the crystal grain, whereby the magneticproperties for the thin sendust sheet become nearly the same as inconventional ingot material, whereupon thin sendust sheet havingoutstanding magnetic properties can be fabricated, as has beenconfirmed.

It is also possible to perform such machining as cutting and punching onthe raw-material rolled silicon steel sheet, after it is rolled, so thatthin sendust sheet products can be fabricated in various shapes suitableto various applications. Thus the advantage is gained of being able tofabricate, at low cost, thin sendust sheet having high dimensionalprecision and exhibiting outstanding properties.

EMBODIMENTS Embodiment 1

Gas-atomized powders of silicon steel having the compositions andaverage grain sizes given in Table 1 were used for the raw materialpowder for sintered silicon steel sheet. A PVA (polyvinyl alcohol)binder, water, and plasticizer were added, in the amounts indicated inTable 2, to the raw material powders to make slurries. These slurrieswere granulated with a completely sealed spray drier apparatus, innitrogen gas, with the hot gas inlet temperature set at 100° C. and theoutlet temperature set at 40° C.

Next, after green-molding the granulated powders having an average grainsize of approximately 100 μm with a compression press under a pressureof 2 tons/cm² to the shapes noted in Table 3, binder removal andsintering at sintering temperatures as noted in Table 3 were performedin a vacuum and in hydrogen to yield sintered bodies having thedimensions noted in Table 4. The residual oxygen amounts, residualcarbon amounts, average crystal grain sizes, and relative densities inor of the sintered bodies obtained are listed in Table 4.

After cold-rolling the sintered bodies having the dimensions listed inTable 4 with two-stage rollers having diameters of 60 mm at a rollercircumferential speed of 60 mm/sec until a rolling ration of 50% wasattained, cold rolling was performed with four-stage rollers havingdiameters of 20 mm at the same roller circumferential speed, down to0.10 mm. The rolled conditions are listed in Table 5.

After rolling, furthermore, rings measuring 20 mm Ø×10 mm Ø×0.1 mm twere punched out. These rings were heat treated at the annealingtemperatures noted in Table 5, after which the DC magnetic propertiesand iron loss at a frequency of 5 kHz were measured. The results arelisted in Table 6. In terms of the rolled conditions noted in Table 5, ⊚indicates very good, ◯ indicates good, Δ indicates the occurrence ofcracking at the end surfaces of the rolled sheet, and X indicates theoccurrence of cracking over the entire surface.

Embodiment 2

After high-frequency melting the molten silicon steel of thecompositions noted in Table 1, the melts were made to flow intowater-cooled casting molds in thin-sheet form having a casting thicknessof 5 mm and quick cooling was performed to fabricate steel sheetmeasuring 50×50×5 mm. Steel sheet cooled slowly without water coolingwas also fabricated for comparison. The residual oxygen amounts,residual carbon amounts, average crystal grain sizes, and relativedensities of the steel sheet obtained are indicated in Table 4.

Prior to cold rolling, in order to prevent cracking during rolling,steel sheets were prepared from which surface irregularities wereremoved by processing both sides of the 50×50 mm sheets with a surfacegrinder. The rolled conditions after that are noted in Table 7, where ◯indicates good and X indicates the occurrence of cracks in the entiresurface.

After rolling under the same cold rolling conditions as in the firstembodiment, heat treatment was performed at the annealing temperatureslisted in Table 7, after which the DC magnetic properties and iron lossat a frequency of 5 kHz were measured. The results are given in Table 8,comparing them with the magnetic properties of a ingot materialfabricated without water cooling.

TABLE 1 Average Minute composition (wt %) Si powder Metal element Samplecontent grain size Residual O, C Element Added No. (wt %) (μm) O C nameamount Powder raw material 1 3.0 40 0.031 0.025 N/A — 2 6.5 30 0.0430.025 N/A — 3 6.5 30 0.052 0.029 V  0.02 4 6.5 30 0.065 0.030 Al 0.5 56.5 30 0.070 0.032 Ti  1.00 6 10.0 140  0.027 0.013 Al 0.5 Molten rawmaterial 7 6.5 — 0.004 0.001 Al 0.5

TABLE 2 Amount of binder added Polymer Plasticizer Water Embodiment 1Polyvinyl alcohol Glycerin Water :1.0 wt % :0.1 wt % :54 wt %

TABLE 3 Molded body Binder removal conditions Sintering conditionsSample dimensions Temperature Time Temperature Time No. No. (mm)Atmosphere (° C.) (H) Atmosphere (° C.) (H) Embodiment 1 1 1 60 × 60 ×1.2 Vacuum 500 2 Vacuum 1200 3 2 1 60 × 60 × 5.8 Vacuum 500 2 Vacuum1200 3 3 1 60 × 60 × 11.8 Vacuum 500 2 Vacuum 1200 3 4 2 60 × 60 × 1.2Vacuum 500 2 Vacuum 1200 3 5 3 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1200 36 4 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1200 3 7 5 60 × 60 × 1.2 Vacuum500 2 Vacuum 1200 3 8 4 60 × 60 × 1.2 Hydrogen 500 2 Hydrogen 1200 3 9 460 × 60 × 5.8 Vacuum 500 2 Vacuum 1200 3 10 4 60 × 60 × 11.8 Vacuum 5002 Vacuum 1200 3 11 4 60 × 60 × 5.8 Vacuum 500 2 Vacuum 1050 3 12 4 60 ×60 × 5.8 Vacuum 500 2 Vacuum 1300 3 13 6 60 × 60 × 5.8 Vacuum 500 2Vacuum 1150 3

TABLE 4 Residual oxygen and carbon Average Pre-rolling amounts crystalRelative Sample dimensions Parallelism (wt %) grain size density No. No.(mm) (mm) O C (μm) (%) Embodiment 1 1 1 50 × 50 × 1.0 0.26 0.1100 0.00482 99 2 1 50 × 50 × 5.0 0.15 0.1150 0.004 78 99 3 1 50 × 50 × 10.0 0.120.1150 0.004 75 99 4 2 50 × 50 × 1.0 0.25 0.1200 0.005 120 99 5 3 50 ×50 × 1.0 0.26 0.1200 0.005 125 99 6 4 50 × 50 × 1.0 0.29 0.1400 0.005150 99 7 5 50 × 50 × 1.0 0.26 0.1600 0.005 182 99 8 4 50 × 50 × 1.0 0.380.0750 0.001 95 98 9 4 50 × 50 × 5.0 0.14 0.1200 0.005 125 99 10 4 50 ×50 × 10.0 0.10 0.1150 0.005 135 99 11 4 50 × 50 × 5.0 0.18 0.1200 0.00545 91 12 4 50 × 50 × 5.0 0.15 0.1600 0.005 430 99 13 6 50 × 50 × 5.00.16 0.1400 0.006 290 99 Embodiment 2 14 7 50 × 50 × 5.0 0.54 0.0040.001 240 100 15 7 50 × 50 × 5.0 0.06 0.004 0.001 240 100 16 7 50 × 50 ×5.0 0.06 0.004 0.001 2800 100

TABLE 5 Average Annealing crystal grain Sample Rolled temperature sizeNo. No. condition (° C.) × 3H (μm) Embodiment 1  1 1 ⊚ 1250  900  2 1 ⊚1250 1100  3 1 Δ 1250 1500  4 2 ⊚ 1260 1000  5 3 ⊚ 1220 1200  6 4 ⊚ 12001700  7 5 ⊚ 1180 1400  8 4 ⊚ 1200 1600  9 4 ⊚ 1230 1800 10 4 Δ 1260 200011 4 X — — 12 4 X — — 13 6 ◯ 1250 2300

TABLE 6 Relative Magnetic properties and iron loss density No. μm Bs(T)iHc(Oe) η(W/kg) (%) Embodiment 1  1  9000 1.41 0.35 21 100  2 10000 1.430.31 18 100  3 12000 1.47 0.28 16 100  4 11000 1.27 0.20 17 100  5 150001.25 0.18 15 100  6 18000 1.21 0.15 13 100  7 17000 1.18 0.16 14 100  817000 1.21 0.16 14 100  9 17000 1.21 0.15 13 100 10 18000 1.21 0.15 13100 11 — — — — — 12 — — — — — 13 11000 1.00 0.17 21 100

TABLE 7 Annealing Crystal Parallel- Rolled temper- grain size Sample ismcondi- ature after rolling No. No. (mm) tion (° C.) × 3H (μm) Embodiment2 14 7 0.54 X — — 15 7 0.06 ◯ 1230 1600 16 7 0.06 X — —

TABLE 8 Relative Magnetic properties and iron loss density No. μm Bs(T)iHc(Oe) η(W/kg) (%) Embodiment 2 14 — — — — — 15 16000 1.18 0.1717 14100 16 — — — — —

Embodiment 3

After performing high-frequency melting and forming ingots from rawmaterial powder for sintered silicon steel sheet to form Fe—Si compoundshaving the compositions noted in Table 9, these were coarse-crushed andthen jet-mill pulverized to make powders having the average grain sizesindicated in Table 9.

After mixing the Fe—Si compound powder and carbonyl iron powder in theproportions noted in Table 10, these were mixed with a V cone. A PVA(polyvinyl alcohol) binder, water, and plasticizer were added, in theamounts indicated in Table 11, to the mixed powders to make slurries.These slurries were granulated with a completely sealed spray drierapparatus, in nitrogen gas, with the hot gas inlet temperature set at100° C. and the outlet temperature set at 40° C.

After green-molding the granulated powders having an average grain sizeof approximately 100 pm with a compression press under a pressure of 2tons/cm2 to the shapes noted in Table 12, binder removal and sinteringat sintering temperatures as noted in Table 12 were performed in avacuum and in hydrogen to yield sintered bodies having the dimensionsnoted in Table 13. The ratios of iron-rich phase content, residualoxygen amounts, residual carbon amounts, and relative densities in or ofthe sintered bodies obtained are listed in Table 13 . The iron-richphase content ratio was evaluated relatively according to the ratiobetween the maximum x-ray diffraction strength characteristic of theFe—Si compound and the (110) diffraction strength of the silicon steelhaving a body centered cubic structure (bcc).

After cold-rolling the sintered bodies having the dimensions listed inTable 13 with two-stage rollers having diameters of 60 mm at a rollercircumferential speed of 60 mm/sec until a rolling ratio of 50% wasattained, cold rolling was performed with four-stage rollers havingdiameters of 20 mm at the same roller circumferential speed, down to0.10 mm. The rolled conditions are listed in Table 14. In terms of therolled conditions noted in Table 14,  indicates very good, ◯ indicatesgood, Δ indicates the occurrence of cracking at the end surfaces of therolled sheet, and X indicates the occurrence of cracking over the entiresurface.

After rolling, furthermore, rings measuring 20 mm ø×10 mm ø×0.1 mm twere punched out. These rings were heat treated at the annealingtemperatures noted in Table 14, after which the DC magnetic propertiesand iron loss at a frequency of 5 kHz were measured. The results arelisted in Table 15. The magnetic properties of Fe-6.5Si ingot materialare listed in Table 15 to provide an example for comparing magneticproperties.

TABLE 9 Average powder Minute composition (wt %) Raw Silicon grain Metalelement material content size Residual O, C Element Added No. (wt %)Compound (μm) O C name amount Fe—Si compound powder 1 20.1 Fe₂Si(β) 6.40.040 0.007 N/A — 2 33.5 FeSi(ε) 4.8 0.060 0.013 N/A — 3 33.5 FeSi(ε)4.9 0.060 0.014 V 0.10 4 33.5 FeSi(ε) 4.8 0.065 0.015 Al 2.60 5 33.5FeSi(ε) 4.8 0.080 0.018 Ti 5.10 6 50.1 FeSi₂(ζβ) 3.5 0.092 0.025 Al 3.85Fe powder 7 — Fe 5.8 0.240 0.023 N/A —

TABLE 10 Fe—Si Compound powder and iron powder mixture weightsComposition Minute composition Raw Sample (wt %) Element Contentmaterial Fe-Si Fe No Fe Si name (wt %) No. (wt %) (wt %) Embodiment 3 197 3 N/A — 1 14.9 85.1 2 93.5 6.5 N/A — 1 32.3 67.7 3 93.5 6.5 N/A — 219.4 80.6 4 93.5 6.5 V 0.02 3 19.4 80.6 5 93.5 6.5 Al 0.50 4 19.4 80.6 693.5 6.5 Ti 1.00 5 19.4 80.6 7 93.5 6.5 Al 0.50 6 14.9 85.1 8 90 10 N/A— 6 20.0 80.0

TABLE 11 Amount of binder added Polymer Plasticizer Water Embodiment 3Polyvinyl alcohol Glycerin Water :0.5 wt % :0.1 wt % :54 wt %

TABLE 12 Molded body Binder removal conditions Sintering conditionsSample dimensions Temperature Time Temperature Time No. No. (mm)Atmosphere (° C.) (H) Atmosphere (° C.) (H) Embodiment 3 1 1 60 × 60 ×1.2 Vacuum 500 2 Vacuum 1100 2 2 1 60 × 60 × 5.8 Vacuum 500 2 Vacuum1100 2 3 1 60 × 60 × 11.8 Vacuum 500 2 Vacuum 1100 2 4 2 60 × 60 × 1.2Vacuum 500 2 Vacuum 1050 2 5 3 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1040 26 4 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1030 2 7 5 60 × 60 × 1.2 Vacuum500 2 Vacuum 1200 2 8 5 60 × 60 × 1.2 Vacuum 500 2 Vacuum 950 2 9 5 60 ×60 × 1.2 Vacuum 500 2 Vacuum 1000 2 10 6 60 × 60 × 1.2 Vacuum 500 2Vacuum 1000 2 11 6 60 × 60 × 1.2 Hydrogen 500 2 Hydrogen 1000 2 12 7 60× 60 × 1.2 Vacuum 500 2 Vacuum 1000 2 13 3 60 × 60 × 5.8 Vacuum 500 2Vacuum 1040 2 14 3 60 × 60 × 11.8 Vacuum 500 2 Vacuum 1040 2 15 8 60 ×60 × 1.2 Vacuum 500 2 Vacuum 1000 2 16 8 60 × 60 × 5.8 Vacuum 500 2Vacuum 1000 2

TABLE 13 Residual oxygen and carbon X-ray Relative Raw Pre-rollingamounts diffraction sintering material dimensions Parallelism (wt %)strength density No. No. (mm) (mm) O C ratio (%) Embodiment 3 1 1 50 ×50 × 1.0 0.32 0.1500 0.005 0.012 96 2 1 50 × 50 × 5.0 0.17 0.1500 0.0050.012 96 3 1 50 × 50 × 10.0 0.14 0.1500 0.005 0.012 96 4 2 50 × 50 × 1.00.34 0.1400 0.006 0.024 95 5 3 50 × 50 × 1.0 0.35 0.1600 0.008 0.020 956 4 50 × 50 × 1.0 0.31 0.1600 0.008 0.018 96 7 5 50 × 50 × 1.0 0.290.1700 0.008 0.001 99 8 5 50 × 50 × 1.0 0.30 0.1700 0.008 0.086 87 9 550 × 50 × 1.0 0.34 0.1700 0.008 0.014 96 10 6 50 × 50 × 1.0 0.23 0.18000.008 0.017 95 11 6 50 × 50 × 1.0 0.25 0.0840 0.001 0.017 95 12 7 50 ×50 × 1.0 0.33 0.1900 0.010 0.025 94 13 3 50 × 50 × 5.0 0.17 0.1600 0.0080.017 96 14 3 50 × 50 × 10.0 0.13 0.1600 0.008 0.018 96 15 8 50 × 50 ×1.0 0.37 0.1900 0.013 0.045 95 16 8 50 × 50 × 5.0 0.20 0.1900 0.0130.043 95

TABLE 14 Raw Annealing Average crystal material Rolled temperature grainsize No. No. condition (° C.) × 3H (μm) Embodiment 3  1 1 ⊚ 1200 1000  21 ◯ 1250 1200  3 1 X — —  4 2 ⊚ 1260 1100  5 3 ⊚ 1220 1300  6 4 ⊚ 12001900  7 5 X — —  8 5 X — —  9 5 ⊚ 1200 1800 10 6 ⊚ 1200 1700 11 6 ⊚ 12001600 12 7 ⊚ 1280 2000 13 3 ◯ 1250 1800 14 3 X — — 15 8 ⊚ 1220 2300 16 8◯ 1250 2500 Comparison Fe-6.5Si Ingot — 3600 material

TABLE 15 Raw Relative material Magnetic properties and iron loss (η)density No No. μm Bs(T) iHc(Oe) η(W/kg) (%) Embodi- ment 3  1 1  90001.41 0.35 21 100  2 1 11000 1.43 0.32 18 100  3 1 — — — — —  4 2 100001.24 0.21 18 100  5 3 13000 1.23 0.19 16 100  6 4 16000 1.21 0.16 14 100 7 5 — — — — —  8 5 — — — — —  9 5 17000 1.21 0.16 14 100 10 6 160001.21 0.16 14 100 11 6 15000 1.21 0.17 15 100 12 7 17000 1.22 0.15 13 10013 3 16000 1.21 0.15 14 100 14 3 — — — — — 15 8 10000 1.00 0.19 20 10016 8 11000 1.00 0.18 22 100 Comparison Fe-6.5Si 16000 1.22 0.14 14 100100 100

Embodiment 4

The Fe—Si—La compound powders having the compositions and average grainsizes noted in Table 16 were used for the lanthanum sintered siliconsteel raw material powder. These Fe—Si—La compound powders were firstmelted by high-frequency melting lanthanum and the Fe—Si compounds notedin Table 16 and made into alloy ingots. The ingots were coarse-crushedand then jet-mill pulverized. The carbonyl iron powders having thecomposition and average grain size noted in Table 16 were used for theiron powder. The β, ε, and ζβ symbols in the “Compound” column in Table16 indicate the type of crystal.phase in the Fe—Si compound.

Next, the Fe—Si—La compound powder and iron powder were mixed in theproportions indicated in Table 17 and mixed together in a V cone. Rawmaterials No. 8 and No. 9 in Table 17 contain no lanthanum and are givenas comparison examples.

To the mixture powders so obtained were added a PVA (polyvinyl alcohol)binder, water, and plasticizer, in the amounts indicated in Table 11, tomake slurries. These slurries were granulated with nitrogen gas, using acompletely sealed spray drier apparatus, with the hot gas inlettemperature set at 100° C. and the outlet temperature set at 75° C. Theaverage grain size of the granulated powders was approximately 80 μm.

Next, the granulated powders noted above were green-molded using acompression press under a pressure of 2 tons/cm². The dimensions of themoldings produced are given in Table 18. Sintering was then performedunder the binder removing conditions and sintering temperatureconditions noted in Table 18, in a vacuum and in hydrogen, yielding thesintered bodies having the dimensions indicated in Table 19. Theresidual oxygen amounts, residual carbon amounts, average crystal grainsizes, and relative densities of the sintered bodies are noted in Table19. In Table 20 are noted the results of evaluating the rolledcondition, annealing temperatures, average crystal grain sizes of rolledsilicon steel sheet, DC magnetic properties, DC resistivity ρ, andmeasured densities. The symbols in the “Rolled Condition” column are thesame as those used in the first embodiment.

Also given in Table 20, as comparison examples, are the results ofevaluating the properties of an ingot material of silicon steel having asilicon content of 3.0 wt % and of an ingot material of silicon steelhaving a silicon content of 6.5 wt %.

TABLE 16 Average powder Minute composition (wt %) Raw Silicon grainMetal element material content size Residual O, C Element Added No. (wt%) Compound (μm) O C name amount Fe—Si—La compound powder 1 20.1Fe₂Si(β) 6.4 0.040 0.070 La 0.67 2 33.5 FeSi(ε) 4.9 0.060 0.014 La 0.263 33.5 FeSi(ε) 4.8 0.065 0.015 La 2.63 4 33.5 FeSi(ε) 4.8 0.080 0.018 La5.25 5 33.5 FeSi(ε) 4.5 0.105 0.029 La 10.5 6 33.5 FeSi(ε) 4.1 0.1160.035 La 12.9 7 50.1 FeSi₂(ζβ) 3.5 0.092 0.025 La 3.85 Fe—Si powder 820.1 Fe₂Si(β) 6.6 0.038 0.007 N/A — 9 33.5 FeSi(ε) 4.8 0.060 0.013 N/A —Fe powder 10 — Fe 5.8 0.240 0.023 N/A — Note: The β, ε, and ζβ symbolsin the parentheses () in the “Compound” column indicate the type ofcrystal phase in the Fe-Si compound.

TABLE 17 Fe—Si—La compound powder and iron powder mixture weightsComposition La Raw Sample (wt %) content Material Fe—Si—La No Fe Si (wt%) No. (wt %) Fe (wt %) Embodiment 4 1 97 3 0.1 1 14.9 85.1 2 93.5 6.50.05 2 19.4 80.6 3 93.5 6.5 0.50 3 19.4 80.6 4 93.5 6.5 1.0 4 19.4 80.65 93.5 6.5 2.0 5 19.4 80.6 6 93.5 6.5 2.4 6 19.4 80.6 7 90 10 0.77 720.0 80.0 Comparison 8 97 3 0.0 8 14.9 85.1 9 93.5 6.5 0.0 9 19.4 80.6

TABLE 18 Molded body Binder removal conditions Sintering conditionsSample dimensions Temperature Time Temperature Time No. No. (mm)Atmosphere (° C.) (H) Atmosphere (° C.) (H) Embodiment 4 1 1 60 × 60 ×1.2 Vacuum 500 2 Vacuum 500 2 2 2 60 × 60 × 1.2 Vacuum 500 2 Vacuum 5002 3 3 60 × 60 × 1.2 Vacuum 500 2 Vacuum 500 2 4 3 60 × 60 × 5.8 Vacuum500 2 Vacuum 500 2 5 3 60 × 60 × 11.8 Vacuum 500 2 Vacuum 500 2 6 3 60 ×60 × 1.2 Hydrogen 500 2 Hydrogen 500 2 7 4 60 × 60 × 1.2 Vacuum 500 2Vacuum 500 2 8 5 60 × 60 × 1.2 Vacuum 500 2 Vacuum 500 2 9 6 60 × 60 ×1.2 Vacuum 500 2 Vacuum 500 2 10 7 60 × 60 × 1.2 Vacuum 500 2 Vacuum 5002 Comparison 11 8 60 × 60 × 1.2 Vacuum 500 2 Vacuum 500 2 12 9 60 × 60 ×0.6 Vacuum 500 2 Vacuum 500 2 13 9 60 × 60 × 1.2 Vacuum 500 2 Vacuum 5002

TABLE 19 Residual oxygen and carbon Average Relative Raw Pre-rollingamounts crystal sintering Sample material dimensions Parallelism (wt %)grain size density No. No. (mm) (mm) O C (μm) (° C.) Embodiment 4 1 1 50× 50 × 1.0 0.35 0.1700 0.005 82 98 2 2 50 × 50 × 1.0 0.38 0.1700 0.006120 96 3 3 50 × 50 × 1.0 0.32 0.2200 0.008 140 96 4 3 50 × 50 × 5.0 0.180.2100 0.008 140 96 5 3 50 × 50 × 10.0 0.14 0.2000 0.008 130 96 6 3 50 ×50 × 1.0 0.37 0.0860 0.002 200 97 7 4 50 × 50 × 1.0 0.33 0.2500 0.009150 96 8 5 50 × 50 × 1.0 0.42 0.2800 0.010 170 96 9 6 50 × 50 × 1.0 0.390.3100 0.012 190 96 10 7 50 × 50 × 1.0 0.48 0.2400 0.008 90 96Comparison 11 8 50 × 50 × 1.0 0.37 0.1500 0.005 74 98 12 9 50 × 50 × 0.50.63 0.2100 0.005 95 97 13 9 50 × 50 × 1.0 0.34 0.1800 0.005 110 97

TABLE 20 Sintered Body Cold-Rolled Conditions and Post-AnnealingMagnetic Properties Average Magnetic properties and Raw Annealingcrystal electrical resistivity Relative Sample material Rolledtemperature grain size Bs iHc ρ × 10⁻⁷ density No. No. conditions (° C.)(μm) μm (T) (Oe) (Ωm) (%) Embodiment 4 1 1 ⊚ 1150 1000  8000 1.40 0.37 3.8 100 2 2 ⊚ 1200 1300 11000 1.41 0.32  9.4 100 3 3 ⊚ 1200 1500 110001.39 0.26 13.2 100 4 3 ◯ 1200 1600 11000 1.38 0.24 13.5 100 5 3 X — — —— — — — 6 3 ⊚ 1170 2000 12000 1.38 0.20 13.2 100 7 4 ⊚ 1250 2400 140001.34 0.16 24.2 100 8 5 ⊚ 1250 2800 15000 1.32 0.14 68.2 100 9 6 X — — —— — — — 10 7 ⊚ 1250 2500 11000 1.00 0.17 20.2 100 Comparison 11 8 ⊚ 1150 850  6500 1.40 0.45  2.9 100 12 9 X — — — — — — — 13 9 ⊚ 1200 120011000 1.43 0.32  8.6 100 Comparison Fe-3.0Si Ingot — 2700  9800 1.430.35  2.1 100 material Fe-6.5Si Ingot — 3600 18000 1.42 0.14  7.2 100material Note: The annealing temperature noted is the optimumheat-treatment temperature.

Embodiment 5

For the raw material powder for sintered silicon steel sheet,high-frequency melting was done and ingots were made to form the Fe—Sicompounds and Fe—Si—Al compounds noted in Table 21. These ingots werethen coarse-crushed and jet-mill pulverized to make powders having theaverage grain sizes noted in Table 21.

For the steel powder, carbonyl iron powder having the composition andaverage grain size noted in Table 21 was used. The Fe—Si compounds orFe—Si—Al compounds were mixed with the carbonyl iron powder in theproportions noted in Table 22 and then mixed together in a V cone.

For the powders of the desired composition, moreover, gas-atomizedpowders having the compositions and average grain sizes noted in Table23 were used. To the raw material powders were added a PVA (polyvinylalcohol) binder, water, and plasticizer, in the amounts indicated intable 24, to make slurries. These slurries were pulverized with acompletely sealed spray drier apparatus, using nitrogen gas, with thehot gas inlet temperature set at 100° C. and the outlet temperature setat 40° C.

After green-molding the granulated powders having an average grain sizeof approximately 80 μm with a compression press under a pressure of 2tons/cm² to the shapes noted in Table 25, binder removal and sinteringat sintering temperatures as noted in Table 26 were performed in avacuum to yield sintered bodies having the dimensions noted in Table 26.The parallelism (in Table 26), residual oxygen amounts, residual carbonamounts, average crystal grain sizes, and relative densities in or ofthe sintered bodies obtained are listed in Table 27.

After cold-rolling the sintered bodies having the dimensions listed inTable 26 with two-stage rollers having outer diameters of 60 mm at aroller circumferential speed of 60 mm/sec until a rolling ration of 50%was attained, cold rolling was performed with four-stage rollers havingouter diameters of 20 mm at the same roller circumferential speed, downto the thicknesses indicated ink Table 28. The rolled conditions arelisted in Table 28.

After rolling, 20 Ø×10 Ø rings were punched out, aluminum wasvacuum-deposited on both sides of the steel sheet in the thicknessesnoted in Table 29, heat treatment was performed at the annealingtemperatures indicated in Table 29, and the DC magnetic properties weremeasured. The results are noted in Table 30. The rolled conditions notedin Table 28 are the same as in the first embodiment.

Embodiment 6

After high-frequency melting molten silicon steel having thecompositions noted in Table 23, this was made to flow into awater-cooled thin-sheet-form casting mold having a thickness of 5 mm andthen made into quick-cooled 50×50×5 mm steel sheet as well as steelsheet slow-cooled without quick cooling. The residual oxygen amounts,residual carbon amounts, average crystal grain sizes, and relativedensities of the steel sheet obtained are noted in Table 27.

Prior to cold rolling, in order to prevent cracking during rolling,steel sheet was prepared from which surface irregularities were removedby processing both 50×50 mm sides with a surface grinder (embodiment No.18 and No. 19). A steel sheet was also prepared on which no grinding wasdone (embodiment No. 17). These were rolled to the thicknesses indicatedin Table 28 under the same cold rolling conditions as in Embodiment 1.The results are noted in Table 28.

After rolling, 20 Ø×10 Ø rings were punched out, aluminum was vapordeposited on both sides of the steel sheet to the thicknesses indicatedin Table 29, heat treatment was performed at the annealing temperaturesindicated in Table 29, and the DC magnetic properties were measured. Theresults are noted in Table 30 in comparison with the magnetic propertiesof the ingot material without water cooling.

As an example for magnetic property comparison, the magnetic propertiesof ordinary Fe-6.5Si and sendust alloy ingot material are noted in Table30

TABLE 21 Average Residual O, C Raw Silicon Aluminum grain amountsmaterial content content size (wt %) No. (wt %) (wt %) Compound (μm) O CFe—Si—Al compound powder 1 20.1 0.0 Fe₂Si(β) 6.4 0.040 0.007 2 33.5 0.0FeSi(ε) 4.8 0.060 0.013 3 33.5 2.0 FeSi(ε) 4.9 0.090 0.017 4 33.5 6.0FeSi(ε) 4.7 0.120 0.018 5 50.1 1.0 FeSi₂(ζβ) 3.6 0.130 0.025 Fe powder 6— — Fe 5.8 0.240 0.023 Note: The β, ε, and ζβ symbols in the parentheses() in the “Compound” column indicate the type of crystal phase in theFe-Si compound.

TABLE 22 Fe—Si—Al compound powder and iron Composition powder mixtureweights (wt %) Sample (wt %) Raw material Fe—Si—Al No. Fe Si Al No. (wt%) Fe (wt %) Embodiment 5 1 91.7 8.3 0.0 1 41.3 58.7 2 90.0 10.0 0.0 129.9 70.1 3 88.3 11.7 0.0 2 34.9 65.1 4 89.4 10.0 0.6 3 29.9 70.1 5 88.210.0 1.8 4 29.9 70.1 6 89.8 10.0 0.2 5 20.0 80.0

TABLE 23 Average Residual O, C Silicon Aluminum powder grain amountsSample content content size (wt %) No. (wt %) (wt %) (μm) O C Powder rawmaterial  7  8.3 0.0 25 0.067 0.027  8 10.0 0.0 30 0.089 0.027  9 11.70.0 28 0.103 0.030 10 10.0 2.0 30 0.120 0.033 11 10.0 3.0 30 0.150 0.045Molten raw material 12 10.0 1.0 — 0.004 0.001

TABLE 24 Amount of binder added Polymer Plasticizer Water Embodiment 5Polyvinyl alcohol Glycerin Water :0.5 wt % :0.1 wt % :54 wt %

TABLE 25 Molded body Binder removal conditions Sintering conditionsSample dimensions Temperature Time Temperature Time No. No. (mm)Atmosphere (° C.) (H) Atmosphere (° C.) (H) Embodiment 5 1 1 60 × 60 ×1.2 Vacuum 500 2 Vacuum 1200 3 2 2 60 × 60 × 1.2 Vacuum 500 2 Vacuum1200 3 3 2 60 × 60 × 5.8 Vacuum 500 2 Vacuum 1200 3 4 2 60 × 60 × 11.8Vacuum 500 2 Vacuum 1200 3 5 3 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1200 36 4 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1200 3 7 5 60 × 60 × 1.2 Vacuum500 2 Vacuum 1200 3 8 5 60 × 60 × 1.2 Vacuum 500 2 Hydrogen 1200 3 9 660 × 60 × 1.2 Vacuum 500 2 Hydrogen 1200 3 10 7 60 × 60 × 1.2 Vacuum 5002 Vacuum 1200 3 11 8 60 × 60 × 1.2 Vacuum 500 2 Hydrogen 1200 3 12 9 60× 60 × 1.2 Vacuum 500 2 Vacuum 1200 3 13 10 60 × 60 × 1.2 Vacuum 500 2Vacuum 1200 3 14 10 60 × 60 × 5.8 Vacuum 500 2 Vacuum 1200 3 15 10 60 ×60 × 11.8 Vacuum 500 2 Vacuum 1200 3 16 11 60 × 60 × 1.2 Vacuum 500 2Vacuum 1200 3

TABLE 26 Sample Pre-rolling dimensions Parallelism No. No. (mm) (mm)Embodiment 5  1 1 50 × 50 × 1.0 0.33  2 2 50 × 50 × 1.0 0.34  3 2 50 ×50 × 5.0 0.18  4 2  50 × 50 × 10.0 0.12  5 3 50 × 50 × 1.0 0.37  6 4 50× 50 × 1.0 0.32  7 5 50 × 50 × 1.0 0.34  8 5 50 × 50 × 1.0 0.36  9 6 50× 50 × 1.0 0.30 10 7 50 × 50 × 1.0 0.34 11 8 50 × 50 × 1.0 0.30 12 9 50× 50 × 1.0 0.35 13 10  50 × 50 × 1.0 0.37 14 10  50 × 50 × 5.0 0.17 1510   50 × 50 × 10.0 0.12 16 11  50 × 50 × 1.0 0.37 Embodiment 6 17 12 50 × 50 × 5.0 0.65 18 12  50 × 50 × 5.0 0.08 19 12  50 × 50 × 5.0 0.09Note 1: Parallelism expresses amount of warping per 50 mm in length.Note 2: Parallelism after surface grinding is noted in embodiment No. 18and No. 19. Note 3: In embodiment No. 19, molten steel sheet slow cooledwithout water cooling is represented.

TABLE 27 Average Residual oxygen and crystal grain Relative carbonamounts (wt %) size density O C (μm) (%) Embodiment 5  1 0.1800 0.007 7299  2 0.2100 0.007 79 99  3 0.2100 0.007 63 99  4 0.2100 0.007 56 99  50.2200 0.008 84 99  6 0.1700 0.010 80 99  7 0.2000 0.010 86 99  8 0.21000.010 370  100   9 0.1800 0.010 90 99 10 0.2000 0.012 113  99 11 0.20000.012 105  99 12 0.1900 0.010 110  99 13 0.2200 0.010 124  99 14 0.22000.010 103  99 15 0.2200 0.010 94 99 16 0.2400 0.012 146  99 Embodiment 617 0.004  0.001 230  100  18 0.004  0.001 230  100  19 0.004  0.0013400   100 

TABLE 28 Thickness Relative Sample after rolling density Rolled No. No.(mm) (%) condition Embodiment 5  1 1 0.1 100 ⊚  2 2 0.1 100 ⊚  3 2 0.9100 ◯  4 2 0.9 — Δ  5 3 0.1 100 ⊚  6 4 0.1 100 ⊚  7 5 0.1 100 ⊚  8 5 0.1100 ⊚  9 6 0.1 100 ⊚ 10 7 0.1 100 ◯ 11 8 0.1 — X 12 9 0.1 100 ⊚ 13 10 0.1 100 ⊚ 14 10  0.9 100 ◯ 15 10  0.9 — Δ 16 11  0.1 — X Embodiment 6 1712  0.9 — Δ 18 12  0.9 100 ⊚ 19 12  0.9 — X

TABLE 29 Thickness of Thickness vapor- Annealing conditions afterdeposited Diffusion Grain growing Sample rolling aluminum filmtemperature temperature No. No. (mm) (μm) Atmosphere (° C. × 3H) (° C. ×3H) Embodiment 5 1 1 0.1 6 Vacuum 1050 1250 2 2 0.1 6 Ar 1100 1250 3 20.9 10  Ar 1150 1300 4 2 — — — — — 5 3 0.1 6 Ar 1100 1250 6 4 0.1 5Vacuum 1050 1250 7 5 0.1 10  Ar 1150 1300 8 5 — — — — — 9 6 0.1 5 Vacuum1100 1250 10 7 0.1 6 Ar 1150 1250 11 8 — — — — — 12 9 0.1 7 Ar 1150 125013 10 0.1 8 Vacuum 1100 1300 14 10 0.9 5 Vacuum 1100 1250 15 10 — — — —— 16 11 — — — — — Embodiment 6 17 12 — — — — — 18 12 0.6 10  Ar 11501300 19 12 — — — — — Comparison 20 — — — — — — 21 — — — — — —

TABLE 30 Average Si, Al crystal composition grain Si Al Magneticproperties No. size (mm) (wt %) (wt %) μ_(i) Bs(T) iHc(Oe) Embodiment 51 1.5 8.0 2.1 4500 1.31 0.09 2 1.3 9.7 2.1 4700 1.14 0.09 3 2.1 10.0 0.4 3200 1.28 0.13 4 — — — — — — 5 1.5 9.7 2.1 4000 1.24 0.10 6 1.8 9.82.4 5700 1.18 0.09 7 2.4 9.6 5.4 28000  1.09 0.03 8 — — — — — — 9 1.79.9 2.0 4700 1.20 0.08 10 1.7 8.0 2.1 4500 1.31 0.09 11 — — — — — — 121.8 11.0  2.4 5000 1.17 0.08 13 2.8 9.7 4.9 18000  1.10 0.04 14 1.6 9.92.4 5200 1.18 0.07 15 — — — — — — 16 — — — — — — Embodiment 6 17 — — — —— — 18 2.5 9.8 2.1 4800 1.11 0.08 19 — — — — — — Comparison 20 — 6.5 —3000 1.22 0.14 21 — 9.6 5.4 32000  1.09 0.03

Embodiment 7

For the raw material powder for sintered silicon steel sheet,high-frequency melting was done and ingots were made to form the Fe—Sicompounds and Fe—Si—Al compounds noted in Table 31. These ingots werethen coarse-crushed and jet-mill pulverized to make powders having theaverage grain sizes noted in Table 31.

For the steel powder, carbonyl iron powder having the composition andaverage grain size noted in Table 31 was used. The Fe—Si compounds orFe—Si—Al compounds were mixed with the carbonyl iron powder in theproportions noted in Tablet 32 and then mixed together in a V cone.

For the powders of the desired composition, moreover, gas-atomizedpowders having the compositions and average grain sizes noted in Table33 were used. To the raw material powders were added a PVA (polyvinylalcohol) binder, water, and plasticizer, in the amounts indicated inTable 24 to make slurries. These slurries were pulverized with acompletely sealed spray drier apparatus, using nitrogen gas, with thehot gas inlet temperature set at 100° C. and the outlet temperature setat 40° C.

After green-molding the granulated powders having an average grain sizeof approximately 80 μm with a compression press under a pressure of 2tons/cm² to the shapes noted in Table 34, binder removal and sinteringat sintering temperatures as noted in Table 34 were performed in avacuum to yield sintered bodies having the dimensions noted in Table 35.The parallelism (in Table 35), ratio of iron-rich phase contained,residual oxygen amounts, residual carbon amounts, average crystal grainsizes, and relative densities in or of the sintered bodies obtained arelisted in Table 36. The iron-rich phase content ratio was evaluatedrelatively according to the ratio between the maximum X-ray diffractionstrength characteristic of the Fe—Si compound and the (110) diffractionstrength of the silicon steel having a body centered cubic structure(bcc).

After cold-rolling the sintered bodies having the dimensions listed inTable 35 with two-stage rollers having outer diameters of 60 mm at aroller circumferential speed of 60 mm/sec until a rolling ration of 50%was attained, cold rolling was performed with four-stage rollers havingouter diameters of 20 mm at the same roller circumferential speed, downto the thicknesses indicated in Table 37. The rolled conditions arelisted in Table 37.

After rolling, 20 Ø×10 Ø rings were punched out, aluminum wasvacuum-deposited on both sides of the steel sheet in the thicknessesnoted in Table 38, heat treatment was performed at the annealingtemperatures indicated in Table 38, and the DC magnetic properties weremeasured. The results are noted in Table 39. The rolled conditions notedin Table 37 are the same as in the first embodiment. As an example formagnetic property comparison, the magnetic properties of ordinaryFe-6.5Si and sendust alloy ingot material are noted in Table 39.

TABLE 31 Alu- Average Residual O, C Raw Silicon minum grain amountsmaterial content content size (wt %) No. (wt %) (wt %) Compound (μm) O CFe—Si—Al compound powder 1 20.1 0.0 Fe₂Si(β) 6.4 0.040 0.007 2 33.5 0.0FeSi(ε) 4.8 0.060 0.013 3 33.5 2.0 FeSi(ε) 4.9 0.090 0.017 4 33.5 6.0FeSi(ε) 4.7 0.120 0.018 5 50.1 1.0 FeSi₂(ζβ) 3.6 0.130 0.025 Fe powder 6— — Fe 5.8 0.240 0.023 Note: The β, ε, and ζβ symbols in the parentheses( ) in the “Compound” column indicate the type of crystal phase in theFe—Si compound.

TABLE 32 Composition Fe—Si—La compound powder and iron Sample (wt %)powder mixture weights(wt %) No. Fe Si Al No. Fe—Si—Al(wt %) Fe(wt %)Embodi- ment 7 1 91.7 8.3 0.0 1 41.3 58.7 2 90.0 10.0 0.0 1 29.9 70.1 388.3 11.7 0.0 2 34.9 65.1 4 89.4 10.0 0.6 3 29.9 70.1 5 88.2 10.0 1.8 429.9 70.1 6 89.8 10.0 0.2 5 20.0 80.0

TABLE 33 Average Residual O,C Silicon Aluminum powder grain amountsSample content content size (wt %) No. (wt %) (wt %) (μm) O C Powder  7 8.3 0.0 25 0.067 0.027 raw  8 10.0 0.0 30 0.089 0.027 material  9 11.70.0 28 0.103 0.030 10 10.0 2.0 30 0.120 0.033 11 10.0 3.0 30 0.150 0.045Molten 12 10.0 1.0 — 0.004 0.001 raw material

TABLE 34 Molded body Binder removal conditions Sintering conditionsSample dimensions Temperature Time Temperature Time No. No. (mm)Atmosphere (° C.) (H) Atmosphere (° C.) (H) Embodiment 7 1 1 60 × 60 ×1.2 Vacuum 500 2 Vacuum 1150 3 2 2 60 × 60 × 1.2 Vacuum 500 2 Vacuum1150 3 3 2 60 × 60 × 5.8 Vacuum 500 2 Vacuum 1150 3 4 2  60 × 60 × 11.8Vacuum 500 2 Vacuum 1100 3 5 3 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1100 36 4 60 × 60 × 1.2 Vacuum 500 2 Vacuum 1100 3 7 5 60 × 60 × 1.2 Vacuum500 2 Vacuum 1100 3 8 5 60 × 60 × 1.2 Vacuum 500 2 Hydrogen 1200 3 9 660 × 60 × 1.2 Vacuum 500 2 Hydrogen 1100 3 10 7 60 × 60 × 1.2 Vacuum 5002 Vacuum 1150 3 11 8 60 × 60 × 1.2 Vacuum 500 2 Hydrogen 1150 3 12 9 60× 60 × 1.2 Vacuum 500 2 Vacuum 1150 3 13 10 60 × 60 × 1.2 Vacuum 500 2Vacuum 1150 3 14 10 60 × 60 × 5.8 Vacuum 500 2 Vacuum 1150 3 15 10  60 ×60 × 11.8 Vacuum 500 2 Vacuum 1150 3 16 11 60 × 60 × 1.2 Vacuum 500 2Vacuum 1150 3

TABLE 35 Pre-rolling Sample dimensions Parallelism No. No. (mm) (mm)Embodiment 7  1 1 50 × 50 × 1.0 0.30  2 2 50 × 50 × 1.0 0.31  3 2 50 ×50 × 5.0 0.15  4 2  50 × 50 × 10.0 0.09  5 3 50 × 50 × 1.0 0.34  6 4 50× 50 × 1.0 0.28  7 5 50 × 50 × 1.0 0.30  8 5 50 × 50 × 1.0 0.32  9 6 50× 50 × 1.0 0.25 10 7 50 × 50 × 1.0 0.32 11 8 50 × 50 × 1.0 0.29 12 9 50× 50 × 1.0 0.31 13 10  50 × 50 × 1.0 0.34 14 10  50 × 50 × 5.0 0.14 1510   50 × 50 × 10.0 0.10 16 11  50 × 50 × 1.0 0.51 Note 1: Parallelismexpresses amount of warping per 50 mm in length.

TABLE 36 Average X-ray Residual oxygen and crystal grain diffusionRelative carbon amounts (wt %) size strength density No. O C (μm) ratio(%) Embodi- ment 7  1 0.1500 0.007 51 0.010 93  2 0.1600 0.006 58 0.01093  3 0.1700 0.007 46 0.010 93  4 0.1600 0.008 41 0.012 90  5 0.16000.008 62 0.014 90  6 0.1700 0.009 60 0.012 91  7 0.1800 0.009 65 0.01091  8 0.0850 0.001 350  0.001 94  9 0.0810 0.001 63 0.012 90 10 0.18000.012 70 0.008 92 11 0.0750 0.001 68 0.007 93 12 0.1900 0.007 71 0.00892 13 0.3000 0.007 74 0.006 93 14 0.1800 0.007 62 0.008 92 15 0.19000.007 64 0.007 92 16 0.1800 0.006 85 0.007 93

TABLE 37 Thickness Relative Sample after rolling density Rolled No. No.(mm) (%) condition Embodiment 7  1 1 0.1 100 ⊚  2 2 0.1 100 ⊚  3 2 0.9100 ◯  4 2 0.9 — Δ  5 3 0.1 100 ⊚  6 4 0.1 100 ⊚  7 5 0.1 100 ⊚  8 5 0.1100 ⊚  9 6 0.1 100 ⊚ 10 7 0.1 100 ◯ 11 8 0.1 — X 12 9 0.1 100 ⊚ 13 10 0.1 100 ⊚ 14 10  0.9 100 ◯ 15 10  0.9 — Δ 16 11  0.1 — X

TABLE 38 Annealing conditions Thickness Thickness of Grain afterdeposited Diffusion growing Sample rolling aluminum temperaturetemperature No. No. (mm) film (μm) Atmosphere (° C. × 3H) (° C. × 3H)Embodiment 7 1 1 0.1 6 Vacuum 1050 1250 2 2 0.1 6 Ar 1100 1250 3 2 0.910  Ar 1150 1300 4 2 — — — — — 5 3 0.1 6 Ar 1100 1250 6 4 0.1 5 Vacuum1050 1250 7 5 0.1 10  Ar 1150 1300 8 5 0.1 10  Vacuum 1150 1300 9 6 0.15 Vacuum 1100 1250 10 7 0.1 6 Ar 1150 1250 11 8 — — — — — 12 9 0.1 7 Ar1150 1250 13 10 0.1 8 Vacuum 1100 1300 14 10 0.9 5 Vacuum 1100 1250 1510 — — — — — 16 11 — — — — —

TABLE 39 Average crystal grain size Si, Al composition Magneticproperties No. (mm) Si(wt %) Al(wt %) μ_(i) Bs(T) iHc(Oe) Embodi- ment 71 1.6 8.0 2.1 4500 1.31 0.09 2 1.4 9.7 2.0 4500 1.14 0.10 3 2.4 10.0 0.4 3200 1.28 0.13 4 — — — — — — 5 1.6 11.0  2.1 2800 1.18 0.15 6 1.79.8 2.4 5800 1.18 0.09 7 2.6 9.6 5.4 28000  1.09 0.03 8 — — — — — — 91.5 9.9 2.0 4700 1.20 0.08 10 1.5 8.0 2.1 4500 1.31 0.09 11 — — — — — —12 2.0 11.0  2.4 5000 1.17 0.08 13 3.1 9.7 5.0 19000  1.10 0.03 14 1.79.9 2.4 5200 1.18 0.07 15 — — — — — — 16 — — — — — — Compar- ison 20 —6.5 — 3000 1.22 0.14 21 — 9.6 5.4 32000  1.09 0.03

INDUSTRIAL APPLICABILITY

Conventionally, silicon steel having 3 wt % or more of silicon in theiron has been considered impossible to cold-roll because, in general,the average crystal grain size is large, on the order of several mm.With the manufacturing method of the present invention, however, byemploying a powder metallurgy fabrication process using powder as thestarting raw material and making the average crystal grain size of asheet-form sintered body or quick-cooled steel sheet 300 μm or less,after crystal grain boundary slip transformation, intra-grain sliptransformation occurs, wherefore cold rolling is made possible.Furthermore, by fabricating a mixed powder wherein pure iron powder andFe—Si powder are mixed together in a prescribed portion with a powdermetallurgy technique, and causing an iron-rich phase to remain in thesintered body, cold rolling is made possible using the plastictransformation of those crystal grains. Moreover, it is evident that,when a minute amount of a non-magnetic metal element such as Ti, V, orAl is added, crystal grain growth can be promoted during annealing, themagnetic properties of the thin steel sheet become almost the same asthat of conventional ingot material, and silicon steel sheet exhibitingoutstanding magnetic properties can beg fabricated.

With the rolled silicon steel sheet according to the present invention,the average crystal grain size is made minute, or iron powder and Fe—Sicompound powder is mixed in a prescribed proportion, an iron-rich phaseis caused to remain during sintering, the sheet thickness is made thinprior to rolling, and the parallelism thereof is enhanced, therebymaking it possible to perform cold rolling and punch machining, anddirectionality is also exhibited, wherefore, after annealing,outstanding magnetic properties are exhibited which are the same asconventional ingot material. Accordingly, in the future, theapplications therefor can be broadened over a wide range to transformersand yoke elements, etc.

With the present invention, moreover, by adding lanthanum to the siliconsteel and causing lanthanum oxides to be deposited in the crystal grainboundaries, electrical resistivity can be manifested at a high levelthat is from several times to nearly ten times higher than when no suchaddition is made. Thus particularly desirable properties can be providedin materials for units requiring low eddy current loss in the face ofmagnetic fields alternating at high frequency, such as high-frequencytransformer cores and the like.

With the present invention, furthermore, using the rolled silicon steelsheet of the present invention made amenable to cold rolling, aftervapor-depositing aluminum, to both sides of the rolled thin sheet, whenheat treatment is performed to cause the aluminum to diffuse andpermeate to the interior of that thin sheet and the crystal grain sizeis simultaneously. coarsened, thin sendust sheet is obtained whichexhibits the same outstanding magnetic properties as ingot material, andextremely thin sendust sheet can be easily mass produced. It is foreseenthat this thin sendust sheet will see dramatically expandingapplications over a wide range that includes-transformers and yokeelements, etc.

What is claimed is:
 1. A method for manufacturing Fe—Si alloy steelcomprising the steps of: providing a sintered body of Fe—Si alloy steelhaving a silicon content of 3 to 10 wt %, an average crystal grain sizeof 300 μm or less and a thickness of 5 mm or less; cold-rolling saidsintered body to provide a cold-rolled sintered body; and annealing saidcold-rolled sintered body.
 2. A method for manufacturing Fe—Si alloysteel comprising the steps of: providing a melt ingot of Fe—Si alloysteel having a silicon content of 3 to 10 wt %, an average crystal grainsize of 300 μm or less and a thickness of 5 mm or less; cold-rollingsaid melt ingot to provide a cold-rolled melt ingot; and annealing saidcold-rolled melt ingot.
 3. The method for manufacturing Fe—Si alloysteel according to claims 1 or 2, wherein said sintered body or meltingot contains 0.05 wt % to 2.0 wt % of lanthanum.
 4. The method formanufacturing Fe—Si alloy steel according to claims 1 or 2, wherein saidsintered body or melt ingot contains 0.01 to 1.0 wt % in single orcompound Ti, Al, V.
 5. The method for manufacturing Fe—Si alloy steelaccording to claim 1, wherein said sintered body is fabricated by apowder metallurgy method wherein sintering is performed after molding bypowder injection molding, green molding, or slip-casting, or by a hotformer and plasma sintering.
 6. The method for manufacturing Fe—Si alloysteel according to claim 2, wherein said melt ingot is cast by makingFe—Si alloy steel to flow into a water-cooled casting mold having acasting thickness of 5 mm or less.